Installation for the heat-treatment of parts

ABSTRACT

The invention relates to an installation for the heat-treatment of parts ( 2 ), which comprises a rotary hearth ( 4 ) that can be rotated in a timed manner and which has an outer and an inner wall ( 4, 5 ) limiting a furnace chamber that is divided up into a heating zone ( 6 ) and at least one treatment zone ( 7  to  9 ) by means of vertically movable doors ( 5   a - 5   e ), the outer wall ( 4 ) in the heating zone ( 6 ) being provided with a closable opening ( 11 ) for charging or discharging the furnace. The installation further comprises a transport device for transporting the parts into or out of the rotary hearth furnace and a quenching device ( 19 ).  
     According to the invention, a second closable opening ( 16 ) is disposed in the outer wall ( 2 ) of the rotary hearth furnace ( 1 ) in the last treatment zone. A sluice ( 17 ) is disposed adjacent to said second opening ( 16 ). The quenching device ( 19 ) is designed as a quenching bath and connected to the rotary hearth furnace by means of the sluice ( 17 ).

The present invention relates to an installation for the heat-treatmentof parts, which comprises a rotary hearth furnace that can be rotated ina timed manner which has an outer and an inner wall limiting a furnacechamber which is divided up into a heating zone and at least onetreatment zone by means of vertically movable doors, the outer wall inthe heating zone being provided with a closable opening for charging anddischarging the furnace. The installation further comprises a transportdevice for transporting the parts into or out of the rotary hearthfurnace and a quenching device.

Such an installation is known from the DE C1 34 27 716. It concerns aninstallation for hardening individual parts comprising a rotary hearthfurnace and a hardening press. The rotary hearth furnace has asluice-like charging or discharging zone which is formed by means ofvertically movable doors arranged on either side of the charging anddischarging opening. Once the furnace door has been opened, the partscan be removed individually from this charging or discharging zone bymeans of a charging and discharging robot and conveyed into thehardening press.

There is need for the installation is to be used more universally, i.e.to permit not only the heat-treating of individual parts but also theheat-treating of entire charges located on charge carriers, e.g. grates.Whole charges of parts are generally quenched in a quenching bath.

The cycle time, i.e. the time between placing a part in the rotaryhearth furnace and removing it from the rotary hearth furnace isrelatively long with the known installation as only one opening is usedfor both charging and discharging. Therefore, it is also necessary tominimise the cycle time.

Therefore, the object of the present invention was to create aninstallation of the type described above which is universal and whichhas a short cycle time.

This object is achieved in the installation described above by thecharacterising features of claim 1.

The rotary hearth furnace has two closable openings which are eitherboth used for charging and discharging or one is used solely forcharging and the other solely for discharging. A sluice is disposedupstream of the second opening. A quenching bath is connected directlyto rotary hearth furnace by means of this sluice. The inventiveinstallation can be used universally. Furthermore, the cycle time can beminimised and thus the hourly throughput of parts increased.

The two openings are disposed next to each other at a smallcircumferential distance, the circumferential distance between the firstand the second opening being preferably substantially 45°. Depending onthe space available, the circumferential distance can also be up to 90°in individual cases.

In a preferred embodiment a sluice for charging the furnace is disposedupstream of the first opening so that the first opening is used solelyfor charging. Consequently, the second opening is used solely fordischarging the furnace.

In one advantageous embodiment, the first opening is disposed verticallyabove the furnace chamber. A charging sluice is disposed upstream of thefirst opening in the vertical direction, said charging sluice beingdesigned as a known elevator sluice, with a transport device for thehorizontal transport of the parts. Thus the opening for charging can bedisposed relatively close or immediately adjacent to the dischargingopening. The advantage of this design is that the furnace chamberavailable for heat treatment can be used optimally.

As heat treatment generally takes place in a controlled atmosphere or ina treatment atmosphere, both the sluice and, if provided, the chargingsluice are of gas-tight design.

The sluices have at least one sluice door which is located substantiallyat right angles to the opening in the outer wall. The sluice door istherefore located in a side wall of the sluice. The quenching bath,which is connected to the rotary hearth furnace by means of the sluice,is thus disposed on the side wall of the sluice.

A second quenching device is preferably connected to the rotary hearthfurnace by means of the sluice. This can be a gas quenching chamber oranother quenching bath. This considerably increases the flexibility ofthe installation as the parts can optionally be quenched at differenttemperatures. The two quenching devices are disposed on the opposingside walls of the sluice.

A transport device in the form of a pusher device is preferably assignedto at least one opening. The charge is transported into the dischargingsluice in a simple manner by means of the pusher device and passed fromthere into the quenching bath which adjoins the discharging sluice. Ifthe first opening is also provided with a charging sluice, a pusherdevice can also be used here. The parts, which are packed in baskets orsimilar containers, are transported into the sluice by means of thepusher device and from there passed into the rotary hearth furnace.

One of the vertically movable doors is located between the first openingand the second opening so that a zone separation takes place betweencharging and discharging.

At least one additional vertically movable door to change the length ofthe heating zone and/or treatment zone is preferably provided. Ifrequired, the additional door can be used for zone separation. All doorscan be controlled and therefore moved individually.

In the phases in which the hearth of the rotary hearth furnace rotates,all doors are normally open, i.e. all doors are simultaneously raised.In the phase in which the hearth does not rotate, all doors which areused for zone separation are closed. If there is no need for zoneseparation using the additional door, this door is also open during thephases in which the hearth is not moving. If the additional door isneeded for zone separation and thus for changing the length of theheating and/or treatment zone, at least one of the doors which waspreviously used for zone separation is kept constantly open during thephase in which the hearth is not moving. Thus the length of the heatingzone and/or treatment zone can be optimised as required for differentheat-treatment processes.

The invention further provides a rotary hearth furnace for theheat-treatment of parts which comprises a rotary hearth which can berotated in timed manner, an outer and an inner wall limiting a furnacechamber which is divided up into a heating zone and at least onetreatment zone by means of vertically movable doors, and a closablecharging and discharging opening which is disposed in the outer walladjacent to the heating zone. The rotary hearth furnace is characterisedin that a second closable charging and discharging opening is disposedin the outer wall adjacent to the heating zone and at a distance to thefirst charging and discharging opening and that the rotary hearth can berotated in both directions.

The invented rotary hearth furnace makes it possible to choose betweentwo charging and discharging options. Both charging and dischargingopenings can be used both for charging and discharging. Both chargingand discharging openings are located adjacent to the heating zone sothat, regardless of which opening is charged, it is ensured that theparts enter the heating zone directly after they have been placed in thefurnace. It is only necessary to change the direction of rotation of therotary hearth accordingly. This considerably improves the functionalityof the rotary hearth furnace.

The heating zone preferably extends over an area of substantially 90°between the first and the second charging and discharging opening.

It is advantageous if at least two treatment zones are provided whicheach adjoin the heating zone and for each of which a different treatmenttemperature and a different treatment atmosphere can be set.

As heat treatment generally takes place in a controlled atmosphere, thesluice is preferably of gas-tight design.

In one preferred embodiment, doors are provided on both sidesimmediately next to the first charging and discharging opening so that acharging and discharging zone is formed which can be heated.

Furthermore, the invention provides an installation which comprises arotary hearth furnace according to the invention, a transport device fortransporting the parts into or out of the rotary hearth furnace and aquenching device, characterised in that a sluice is disposed adjacent tothe second charging and discharging opening, that a second quenchingdevice is provided which is designed as a quenching bath and which isconnected to the second opening of the rotary hearth furnace by means ofthe sluice. This installation is particularly universal as a quenchingdevice is provided at every opening. Every opening is used both forcharging and discharging. The direction of rotation of the rotary hearthfurnace is changed depending on through which of the two openings theparts enter the furnace so that the parts always enter the heating zonefirst.

The invention will now be described in the following by means of apreferred embodiment and the attached drawing.

The drawing shows in

FIG. 1 a schematic top view of a first embodiment of a heat-treatmentinstallation; and, in

FIG. 2, a schematic top view of a second embodiment of a heat-treatmentinstallation.

The installation for hardening parts according to FIG. 1 has a rotaryhearth furnace 1 which can be rotated in a timed manner solely in onedirection, i.e. clockwise. A stationary brick outer wall 2 and an innerwall 3 made of refractory bricks form, together with the rotary hearthand a ceiling not shown, a ring-shaped furnace chamber not shown in thetop view. The furnace chamber is divided by means of doors 5 a-5 d intoa heating zone 6 and three treatment zones 7, 8, 9, i.e. a first and asecond diffusion/carburising zone 7, 9, and carburising zone 8. Thedoors 5 a-5 d can be raised vertically in a manner not shown. The partsare located on charge carriers 10 in the form of grates.

The outer wall is provided, at the beginning of the heating zone 6, witha first closable opening 11 which is disposed downstream of a gas-tightsluice 12 for charging the furnace. The opening 10 between the furnacechamber and the sluice 12 can be opened or closed in the known manner bymeans of a furnace door. The sluice 12 has a sluice door 13 which islocated substantially at right angles to the opening 10 and which isalternately opened or closed for charging. Before the furnace ischarged, the charge carriers 10 with the parts are located in apre-oxidation furnace 14. The charge carriers 10 are pushed out of thesluice 12 into the furnace chamber by means of a first pusher device 15.As the rotary hearth rotates clockwise, the charge carriers 10 enter theheating zone 6 first and from the heating zone 6 the treatment zones 7,8 and 9. The treatment zones are diffusion/carburising zones in whichdifferent treatment temperatures and a different treatment atmospherecan be set. The treatment atmosphere or a neutral gas, for examplenitrogen, can be present in the sluice 12 and the charging sluice.

The outer wall 2 is provided with a second closable opening 16 which isdisposed downstream of a gas-tight sluice 17 for discharging. Thecircumferential distance between the two openings 11 and 16 is approx.45°. A first quenching bath 18 and a second quenching bath 19, each ofwhich has a different temperature, are connected to the sluice 17, oneon each side thereof, by means of sluice doors which are not shown inmore detail and which are located substantially at right angles to theopening 16.

The different charge carriers 10 with the parts are discharged at theend of the last treatment zone by means of a second pusher device 20.Just like charging, discharging is performed in a timed manner. When acharge carrier 10 has arrived at the end of the last treatment zone, thesecond opening 16 opens and the charge carrier 10 is transported bymeans of the pusher device 20 into the sluice 17 and from thereoptionally into one of the two quenching baths 18, 19. Naturally thesecond opening 16 is closed again after each discharge.

A vertically movable door 5 d is located between the first opening 11and the second opening 16 so that charging and discharging take place indifferent zones, i.e. the heating zone 7 and the last treatment zone 9.

Modifications are perfectly possible within the scope of the presentinvention. For example, the circumferential distance between the twoopenings can be more or less than 45°. The circumferential distanceshould be as small as possible but for space reasons it can be up to90°. The second quenching device can be designed as a gas quenchingchamber. Additional doors can be used to change the length of theheating zone and/or the treatment zone.

FIG. 2 shows a rotary hearth furnace 21 which is used for heat-treatingas part of a process for hardening parts 22 and which has a rotaryhearth 23 that can be rotated in a timed manner in both directions. Astationary brick outer wall 24 and an inner wall 25 made of refractorybricks form, together with the rotary hearth 23 and a ceiling not shown,a ring-shaped furnace chamber not shown in the top view. The furnacechamber is divided into a heating zone 27 and three treatment zones 28to 30, i.e. a first and a second diffusion/carburising zone 28, 30, andcarburising zone 29 by means of doors 26 a-26 d. The doors 26 a-26 d canbe raised vertically in a manner not shown.

The outer wall is provided with a first opening 31 for charging anddischarging which is adjoined on both sides by doors 26 a-26 e so that acharging and discharging zone is 32 is formed. A furnace door 33 closesthe first opening 31.

Charging and discharging of the individual parts is performed by acharging and discharging robot 34. Charging is performed in a timedmanner. After the door 26 a has opened, the parts 22 which have beenplaced in the furnace chamber enter the heating zone 27 as the rotaryhearth rotates counterclockwise. The parts 22 on the rotary hearth 23are passed through the treatment zones 28, 29 and 30. Differenttreatment temperatures and different treatment atmospheres can be set inthe diffusions/carburising zones 28, 30. In this charging example, thefirst diffusion/carburising zone 28 is set so that the zone acts as acarburising zone. The second diffusions/carburising zone 30, i.e. thelast treatment zone before discharging, acts as a diffusion zone, i.e.is set so that the C potential in the treatment atmosphere is reduced.The parts which arrive in the charging and discharging zone 32 areremoved individually after the furnace door 33 has opened and quenchedin a hardening device 35. Naturally, the furnace door 33 is closed againafter every discharge.

The outer wall 24 is provided with a second closable opening 36 forcharging or discharging which is disposed at a distance to the firstopening 31 for charging or discharging. The heating zone 27 extends overan area of approx. 90° between the two charging and discharging openings31, 36. The heating zone 27 can be closed immediately after the secondcharging and discharging opening 36 by means of a door 26 b. The twoopenings 31, 36 are therefore each located adjacent to the heating zone27. The direction of rotation of the rotary hearth selected depends onwhich of the two charging and discharging openings 31, 36 is charged. Inany case the parts enter the heating zone after charging.

The second charging and discharging opening 36 is followed by a sluice37 with a cooling bath 38 in the form of an oil bath. In the secondcharging and discharging opening 36, the parts 22, which are located inthe known manner on charge carriers, are put into the furnace chamberand transported clockwise on the rotary hearth 23 through the furnacechamber. In this charging example, the second diffusion/carburising zone30 is set as a carburising zone and the first diffusion/carburising zone28 as a diffusion zone.

Modifications are perfectly possible within the scope of the presentinvention. For example, the heating zone 27 may extend over a largerarea of the furnace chamber.

1-17. (canceled)
 18. An installation for the heat-treatment of partscomprising: a rotary hearth furnace adapted to be rotated in a timedmanner and comprising outer and inner walls for limiting a furnacechamber, said furnace chamber having vertically movable doors adapted todivide up said furnace chamber into a heating zone and at least onetreatment zone; a first opening provided in said outer wall for chargingsaid heating zone, first means for closing said first opening, a secondopening provided in said outer wall for discharging a downstreamtreatment zone, second means for closing said second opening, saidinstallation further comprising: transport means for transporting saidparts into and out of the hearth furnace, quenching bath means forquenching said parts after treatment in said rotary hearth furnace; and,sluice means arranged to connect said second opening and said quenchingbath means.
 19. The installation of claim 18 further including acharging sluice disposed adjacent said first opening.
 20. Theinstallation of claim 19 wherein said sluice means and said chargingsluice have at least one sluice door each disposed substantially atright angles to the associated opening in said outer wall.
 21. Theinstallation of claim 18 wherein the two openings for charging anddischarging are disposed at a circumferential distance of substantially22. The installation as claimed in claim 18 wherein the first openingand the second opening are both provided as charging and dischargingopenings.
 23. The installation as claimed in claim 18, wherein the firstopening for charging is disposed vertically above the furnace chamberand is coupled to a charging sluice disposed vertically above thefurnace chamber and designed as an elevator sluice.
 24. The installationas claimed in claim 18, wherein a second quenching means is connected tothe rotary hearth furnace by means of said sluice means.
 25. Theinstallation as claimed in claim 24, wherein the second quenching meansis selected from the group consisting of a quenching bath and a gasquenching chamber.
 26. The installation as claimed in claim 25, whereinsaid first and second quenching means are operated at differenttemperatures.
 27. The installation as claimed in claim 18, wherein atleast one of said openings for charging and discharging said parts has apusher device associated thereto for conveying said parts through saidopening.
 28. The installation as claimed in claim 18, further comprisinga vertically movable door for changing the length of at least one ofsaid heating and treatment zones.
 29. The installation as claimed inclaim 28, wherein all doors are individually controllable.
 30. Theinstallation as claimed in claim 21, wherein one of said verticallymovable doors is disposed in said circumferential distance ofsubstantially
 31. A rotary hearth furnace for the heat-treatment ofparts comprising: a rotary hearth adapted to be rotated in a timedmanner, an outer and an inner wall for limiting a furnace chamber,vertically movable doors for dividing said furnace chamber up into aheating zone and at least one treatment zone, a first closable openingfor charging and discharging, said first closable opening being disposedin the outer wall adjacent to the heating zone, a second closableopening for charging and discharging, which is disposed in the outerwall adjacent to the heating zone and at a distance to said firstopening, and, said rotary hearth being adapted to be rotated in bothdirections.
 32. A rotary hearth furnace as claimed in claim 31, whereinthe heating zone extends over an area of substantially 90° between saidfirst and said second opening.
 33. The rotary hearth as claimed in claim31, wherein at least two treatment zones are provided each adjoiningsaid heating zone, said at least two treatment zones being adapted to beset to different treatment temperatures and different treatmentatmospheres.
 34. The rotary hearth furnace as claimed in claim 31,wherein doors are provided on both sides immediately next to the openingfor charging and discharging so that a charging and discharging zone isprovided.
 35. An installation for the heat-treatment of parts comprisingthe rotary hearth furnace as claimed in claim 31, further comprising:transport means for transporting the parts into and out of the rotaryhearth furnace, first quenching means, a sluice disposed adjacent thesecond opening, second quenching means designed as a quenching bath andconnected to the second opening for charging and discharging the rotaryhearth furnace.